On my shorty Ruger the warning is on the side of the barrel, my 7.5"s all have the billboard on top of the barrel. The shorties should all be on the side because there isn't enough length on top.
I have serial numbers (last 3) on the inside of the grip frame and the backs of both grip panels (fake ruger ivory) on the shorty.
All of my 7.5" Rugers also have the last 3 or 4 etched into the grip frame but not on the grip panels (they all have wood panels).
I have one gun that is a NIB 7.5 inch ROA that has three digits etched on the face of the cylinder. A 1 4 and 6, they correspond to the chambers. I believe that guns was chosen as proof test model. Its mate with serial +1 doesn't have them on its cylinder.